Method and apparatus for detecting infrared radiation with gain

ABSTRACT

Photodetectors, methods of fabricating the same, and methods using the same to detect radiation are described. A photodetector can include a first electrode, a light sensitizing layer, an electron blocking/tunnelling layer, and a second electrode. Infrared-to-visible upconversion devices, methods of fabricating the same, and methods using the same to detect radiation are also described. An Infrared-to-visible upconversion device can include a photodetector and an OLDE coupled to the photodetector.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/503,317, filed Jun. 30, 2011, the disclosure ofwhich is hereby incorporated by reference in its entirety, including anyfigures, tables, or drawings.

BACKGROUND OF INVENTION

Infrared (IR) light is not visible to the human eye, but an IRphotodetector can detect IR light. IR photodetectors have a wide rangeof potential applications, including night vision, range finding,security, and semiconductor wafer inspections. IR can refer to radiationhaving wavelengths longer than visible light (>0.7 μm) up to about 14μm.

BRIEF SUMMARY

Embodiments of the subject invention relate to a photodetector capableof producing gain (i.e., a photodetector with gain). The photodetectorcan be, for example, an infrared (IR) photodetector. That is, thephotodetector can be sensitive to at least a portion of light in the IRregion. Embodiments of the subject invention also pertain to anIR-to-visible upconversion device. The IR-to-visible upconversion devicecan include a photodetector and an organic light-emitting device (OLED).

In an embodiment, a photodetector with gain can include a firstelectrode, a light sensitizing layer on the first electrode, an electronblocking/tunneling layer on the light sensitizing layer, and a secondelectrode on the electron blocking/tunneling layer.

In another embodiment, a method of fabricating a photodetector with gaincan include: forming a first electrode; forming a light sensitizinglayer on the first electrode; forming an electron blocking/tunnelinglayer on the light sensitizing layer; and forming a second electrode onthe electron blocking/tunneling layer.

In another embodiment, an IR-to-visible upconversion device can includea photodetector with gain and an OLED coupled to the photodetector withgain. The photodetector with gain can include a first electrode, a lightsensitizing layer on the first electrode, an electron blocking/tunnelinglayer on the light sensitizing layer, and a second electrode on theelectron blocking/tunneling layer.

In another embodiment, a method of forming an IR-to-visible upconversiondevice can include: forming a photodetector with gain; forming an OLED;and coupling the OLED to the photodetector with gain. Forming thephotodetector with gain can include: forming a first electrode; forminga light sensitizing layer on the first electrode; forming an electronblocking/tunneling layer on the light sensitizing layer; and forming asecond electrode on the electron blocking/tunneling layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows an absorption spectrum of PbS nanocrystals which can beused as an IR sensitizing layer according to an embodiment of thesubject invention.

FIG. 1B shows a schematic perspective view of a photodetector accordingto an embodiment of the subject invention.

FIG. 2A shows a schematic energy band diagram of a photodetector,according to an embodiment of the subject invention, under appliedvoltage in the dark.

FIG. 2B shows a schematic energy band diagram of a photodetector,according to an embodiment of the subject invention, under appliedvoltage and IR irradiation.

FIG. 3A shows a schematic energy band diagram of a photodetectoraccording to an embodiment of the subject invention.

FIG. 3B shows current vs. voltage characteristics for a photodetectoraccording to an embodiment of the subject invention under dark and photo(1240 nm infrared illumination) conditions.

FIG. 4A shows a plot of gain as a function of applied voltage for aphotodetector according to an embodiment of the subject invention.

FIG. 4B shows a plot of detectivity as a function of applied voltage ona photodetector according to an embodiment of the subject invention.

FIG. 5A shows a schematic energy band diagram of an infrared-to-visibleupconversion device according to an embodiment of the subject invention.

FIG. 5B shows a schematic energy band diagram of an infrared-to-visibleupconversion device according to an embodiment of the subject invention.

FIG. 5C shows a schematic energy band diagram of an infrared-to-visibleupconversion device according to an embodiment of the subject invention.

DETAILED DISCLOSURE

When the terms “on” or “over” are used herein, when referring to layers,regions, patterns, or structures, it is understood that the layer,region, pattern or structure can be directly on another layer orstructure, or intervening layers, regions, patterns, or structures mayalso be present. When the terms “under” or “below” are used herein, whenreferring to layers, regions, patterns, or structures, it is understoodthat the layer, region, pattern or structure can be directly under theother layer or structure, or intervening layers, regions, patterns, orstructures may also be present. When the term “directly on” is usedherein, when referring to layers, regions, patterns, or structures, itis understood that the layer, region, pattern or structure is directlyon another layer or structure, such that no intervening layers, regions,patterns, or structures are present.

When the term “about” is used herein, in conjunction with a numericalvalue, it is understood that the value can be in a range of 95% of thevalue to 105% of the value, i.e. the value can be +/−5% of the statedvalue. For example, “about 1 kg” means from 0.95 kg to 1.05 kg.

When the term “sensitive” is used herein, in conjunction with describinga photodetector being sensitive to a certain type of light or to photonshaving a wavelength of a given value or within a given range, it isunderstood that the photodetector is capable of absorbing the light towhich it is sensitive and generating a carrier. When the term “notsensitive” or “insensitive” is used herein, in conjunction withdescribing a photodetector not being sensitive or being insensitive to acertain type of light or to photons having a wavelength of a given valueor within a given range, it is understood that the photodetector is notable to absorb the light to which it is not sensitive and generate acarrier from the absorption of the light.

Embodiments of the subject invention relate to a photodetector capableof producing gain (i.e., a photodetector with gain). The photodetectorcan be, for example, an infrared (IR) photodetector. That is, thephotodetector can be sensitive to at least a portion of light in the IRregion. In a specific embodiment, the photodetector is sensitive to atleast a portion of the wavelength range from 0.7 μm to 14 μm, inclusiveor non-inclusive. In certain embodiments, the photodetector can besensitive to IR light and can be insensitive to visible light. Forexample, a light sensitizing layer of the photodetector can beinsensitive to at least a portion of the wavelength range from 0.4 μm to0.7 μm. In an embodiment, a light sensitizing layer of the photodetectorcan be insensitive to the entire wavelength range from 0.4 μm to 0.7 μm,inclusive or non-inclusive.

Referring to FIG. 1B, in an embodiment, a photodetector 10 can include afirst electrode 30, a light sensitizing layer 50, an electronblocking/tunneling layer 60, and a second electrode 70. Thephotodetector 10 can also optionally include a substrate 20 and/or ahole blocking layer 40. The substrate 20 can be, for example, a glasssubstrate. Though FIG. 1B includes labels of certain materials for thevarious components, these are intended for demonstrative purposes onlyand embodiments of the subject invention are not limited thereto.

The first electrode 30 can be a cathode, and the second electrode 70 canbe an anode. In an alternative embodiment, the first electrode 30 can bean anode, and the second electrode 70 can be a cathode. In certainembodiments, the first electrode 30 and/or the second electrode 70 canbe transparent to at least a portion of visible and/or at least aportion of IR light, though embodiments are not limited thereto.

The first electrode 30 can include one or more of the followingmaterials: indium tin oxide (ITO), indium zinc oxide (IZO), aluminum tinoxide (ATO), aluminum zinc oxide (AZO), silver, calcium, magnesium,gold, aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO,and CsCO₃/ITO. In a particular embodiment, the first electrode 30 can bean ITO electrode. The second electrode 70 can include one or more of thefollowing materials: ITO, IZO, ATO, AZO, silver, calcium, magnesium,gold, aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO,and CsCO₃/ITO. In a particular embodiment, the second electrode 70 canbe a silver electrode.

In certain embodiments, the photodetector 10 can be an IR photodetectorand the light sensitizing layer 50 can be an IR sensitizing layer. Thatis, the IR sensitizing layer can be sensitive to at least a portion oflight in the IR range. The light sensitizing layer 50 can include, forexample, one or more of the following materials: PbS nanocrystals(quantum dots), PbSe nanocrystals (quantum dots), PCTDA, SnPc, SnPc:C60,AlPcCl, AlPcCl60, TiOPc, TiOPc:C60, PbSe, PbS, InAs, InGaAs, Si, Ge, andGaAs.

FIG. 1A shows an absorption spectrum for PbS nanocrystals as a lightsensitizing layer 50. Referring to FIG. 1A, the PbS nanocrystal lightsensitizing layer shows absorbance in at least a portion of the IRregion.

In an embodiment, the electron blocking/tunneling layer can be a1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC)/MoO₃ stack layer. TheTAPC layer can have a thickness of, for example, 0 nm to 100 nm. TheMoO₃ layer can have a thickness of, for example, 0 nm to 100 nm.

In an embodiment, the photodetector can include a hole blocking layer,and the hole blocking layer can include one or more of the followingmaterials: ZnO, naphthalene tetracarboxylic anhydride (NTCDA),2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP),p-bis(triphenylsilyl)benzene (UGH2), 4,7-diphenyl-1,10-phenanthroline(BPhen), tris-(8-hydroxy quinoline) aluminum (Alq3),3,5′-N,N′-dicarbazole-benzene (mCP), C60,tris[3-(3-pyridyl)-mesityl]borane (3TPYMB), and TiO₂.

In an exemplary embodiment, the photodetector can include a firstelectrode, light sensitizing layer on the first electrode, an electronblocking/tunneling layer on the light sensitizing layer, and a secondelectrode on the electron blocking/tunneling layer. The electronblocking/tunneling layer can be, for example, a TAPC/MoO₃ stack layer,and the TAPC/MoO₃ stack layer can be positioned such that the TAPC layeris in direct contact with the light sensitizing layer and the MoO₃ layeris in direct contact with the second electrode. The light sensitizinglayer can be, for example, an IR sensitizing layer and can include,e.g., PbS quantum dots. In a further embodiment, the photodetector caninclude a hole blocking layer on the first electrode and under the lightsensitizing layer.

FIGS. 2A and 2B demonstrate the operating principle of a photodetectoraccording to an embodiment of the subject invention. Referring to FIG.2A, when a bias is applied in the dark (i.e., no visible and/or IRlight), holes are blocked from the first electrode due to hole blockinglayer, and electrons are blocked from second electrode due to theelectron blocking layer. Referring to FIG. 2B, when the photodetector isirradiated with light (e.g., IR light), the light sensitizing layer(e.g., an IR sensitizing layer) generates electron-hole pairs, and theelectrons flow to the first electrode due to the applied bias. The holesare accumulated in bulk trap sites of the electron blocking/tunnelinglayer, and the accumulated holes reduce the barrier width of theelectron blocking/tunneling layer. Thus, the electron tunneling from thesecond electrode to the light sensitizing layer is enhancedsignificantly, thus producing gain.

FIG. 3A shows a schematic band diagram of a photodetector according toan embodiment of subject invention, and FIG. 3B shows the dark and photocurrent density-voltage (J-V) characteristics for a photodetectoraccording to an embodiment of the subject invention.

FIG. 4A shows a plot of the gain versus the applied voltage for aphotodetector according to the subject invention, and FIG. 4B shows aplot of the detectivity versus the applied voltage for a photodetectoraccording to an embodiment of the subject invention. Referring to FIG.4A, a very high gain can be seen, including a gain of more than 150 atan applied bias of −20 V. Referring to FIG. 4B, the detectivity issaturated to more than 5×10¹² Jones at values of the applied voltage ofless than −18 V.

According to embodiments of the subject invention, a photodetectorexhibits gain at applied bias (i.e., it is a photodetector with gain).The photodetector can exhibit a gain of, for example, about 150 at anapplied bias of −20 V. In various embodiments, the photodetector canexhibit a gain any of the following values or ranges: 2, about 2, atleast 2, 3, about 3, at least 3, . . . , 160, about 160, at least 160(where the “. . . ” represents each number between 3 and 160, “about”each number between 3 and 160, and “at least” each number between 3 and160), or any range having a first endpoint of any number from 2 to 159and a second endpoint of any number from 3 to 160. The gain values andranges of the preceding sentence can be exhibited at any applied voltagevalue from −30 V to 30 V.

Referring to FIGS. 5A-5C, embodiments of the subject invention alsopertain to an IR-to-visible upconversion device 500. The IR-to-visibleupconversion device 500 can include a photodetector 10 and alight-emitting device (LED) 200. In many embodiments, the LED 200 can bean organic LED (OLED). The IR-to-visible upconversion device 500 can bean IR-to-visible upconversion device with gain, and the photodetector 10can be a photodetector with gain. In specific embodiments, theIR-to-visible upconversion device can include a photodetector with gain,as illustrated in FIGS. 1A-1B, 2A-2B, 3A-3B, and 4A-4B and/or asdescribed in connection with the photodetectors of FIGS. 1A-1B, 2A-2B,3A-3B, and 4A-4B. The OLED 200 can include at least one electrode, ahole transporting layer (HTL), a light emitting layer (LEL), and anelectron transporting layer (ETL).

At least one electrode of the OLED 200 can be transparent to at least aportion of visible light and/or at least a portion of IR light, thoughembodiments are not limited thereto.

Each electrode of the OLED 200 can include one or more of the followingmaterials: ITO, 1ZO, ATO, AZO, silver, calcium, magnesium, gold,aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO,CsCO₃/ITO, and a Mg:Ag/Alq3 stack layer, though embodiments are notlimited thereto. The HTL of the OLED 200 can include one or more of thefollowing materials: NPD, TAPC, TFB, TPD, and diamine derivative, thoughembodiments are not limited thereto. The LEL of the OLED 200 can includeone or more of the following materials: Iridium tris(2-phenylpyidine)(Ir(ppy)3), [2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene](MEH-PPV), Tris-(8-quinolinolato) aluminum) (Alq3), andbis[(4,6-di-fluorophenyl)-pyridinate-]picolinate (Flrpic), thoughembodiments are not limited thereto. The ETL of the OLED 200 can includeone or more of the following materials: BCP, Bphen, 3TPYMB, and Alq3,though embodiments are not limited thereto.

In a particular embodiment, the electrode of the OLED 200 is aMg:Ag/Alq3 stack layer. The Mg:Ag layer of the Mg:Ag/Alq3 stack layercan have a composition of, for example, Mg:Ag (10:1) and can have athickness of, for example, less than 30 nm. The Alq3 layer of theMg:Ag/Alq3 stack layer can have a thickness of, for example, from 0 nmto 200 nm.

The photodetector 10 can be a photodetector with gain as describedherein, though only one electrode need be present. That is, thephotodetector 10 can include at least one electrode, a light sensitizinglayer, and an electron blocking/tunneling layer. The photodetector 10can also optionally include a substrate and/or a hole blocking layer.

The electrode can include one or more of the following materials: ITO,IZO, ATO, AZO, silver, calcium, magnesium, gold, aluminum, carbonnanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, and CsCO₃/ITO.

In certain embodiments, the photodetector 10 can be an IR photodetectorand the light sensitizing layer can be an IR sensitizing layer. Thelight sensitizing layer can include, for example, one or more of thefollowing materials: PbS nanocrystals (quantum dots), PbSe nanocrystals(quantum dots), PCTDA, SnPc, SnPc:C60, AlPcCl, AlPcCl:C60, TiOPc,TiOPc:C60, PbSe, PbS, InAs, InGaAs, Si, Ge, and GaAs.

In an embodiment, the electron blocking/tunneling layer can be aTAPC/MoO₃ stack layer. The TAPC layer can have a thickness of, forexample, 0 nm to 100 nm. The MoO₁ layer can have a thickness of, forexample, 0 nm to 100 nm.

In an embodiment, the photodetector can include a hole blocking layer,and the hole blocking layer can include one or more of the followingmaterials: ZnO, NTCDA, BCP, UGH2, BPhen, Alq3, mCP, 3TPYMB, and TiO₂.

Referring to FIG. 5A, in a further embodiment, the IR-to-visibleupconversion device 500 can also include an interconnecting part 100between the photodetector 10 and the OLED 200. The interconnecting part100 can be positioned such that the electron blocking/tunneling layer ofthe photodetector 10 is closer than the light sensitizing layer is tothe interconnecting part 100, and the HTL of the OLED 200 is closer thanthe ETL is to the interconnecting part 100. The photodetector 10 caninclude an electrode under the light sensitizing layer, and thatelectrode can be an anode. The OLED 200 can include an electrode on theETL, and that electrode can be a cathode.

In an embodiment, the interconnecting part 100 can include an HBL 110and an EBL 120. The lowest unoccupied molecular orbital (LUMO) of theHBT, 110 of the interconnecting part 100 can be close to the highestoccupied molecular orbital (HOMO) of the EBL 120 of the interconnectingpart 100. Thus, when a bias is applied, electrons and holes can begenerated in the interconnecting part 100. In an embodiment, the LUMO ofthe HBL 110 of the interconnecting part 100 and the HOMO of the EBL 120of the interconnecting part 100 can be no more than 1 eV apart. In afurther embodiment, the LUMO of the HBL 110 of the interconnecting part100 and the HOMO of the EBL 120 of the interconnecting part 100 can beno more than 0.5 eV apart. That is, the energy difference between theHOMO of the EBL 120 of the interconnecting part 100 and the LUMO of theHBL 110 of the interconnecting part 100 can be 0.5 eV or less. Theinterconnecting part 100 can be positioned within the IR-to-visibleupconversion device 500 such that the HBL 120 of the interconnectingpart 100 can be adjacent to the photodetector 10 and the EBL 120 of theinterconnecting part 100 can be adjacent to the OLED 200. In embodiment,the photodetector 10 can include a second electrode 70 on itsEBL/tunneling layer, and the HBL 120 of the interconnecting part 100 canbe in direct contact with the second electrode 70 of the photodetector10. The second electrode 70 of the photodetector 10 can be a cathode.The second electrode 70 of the photodetector 10 can include one or moreof the following materials: ITO, IZO, ATO, AZO, silver, calcium,magnesium, gold, aluminum, carbon nanotubes, silver nanowire, LT/Al/ITO,Ag/ITO, and CsCO₃/ITO. In a particular embodiment, the second electrode70 of the photodetector 10 can be a silver electrode. Though the dottedline around the interconnecting part 100 in FIG. 5A extends beyond theHBL 110 and the EBL 120, the interconnecting part does not necessarilyinclude any additional components beyond the HBL 110 and the EBL 120. Incertain embodiments, additional components may be present (e.g., one ormore electrodes or substrates).

Referring again to FIGS. 5B and 5C, in an embodiment, the IR-to-visibleupconversion device 500 does not include an interconnecting part 100,and the photodetector 10 is positioned directly adjacent to the OLED200. The OLED 200 can be positioned such that the ETL of the OLED 200 iscloser to the light sensitizing layer of the photodetector 10 than it isto the electron blocking/tunneling layer of the photodetector 10. In aparticular embodiment, the photodetector can include a hole blockinglayer adjacent to the light sensitizing layer, and the ETL of the OLED200 can be positioned adjacent to and in contact with the hole blockinglayer of the photodetector 10. The photodetector 10 can include anelectrode adjacent to and in contact with the electronblocking/tunneling layer, and the OLED 200 can include an electrodeadjacent to and in contact with the HTL. The electrode of thephotodetector 10 can be, for example, a cathode, and the electrode ofthe OLED 200 can be, for example, an anode.

In the IR-to-visible upconversion devices 500 shown in FIGS. 5A-5C, asubstrate (not shown) can also be present. In many embodiments, theIR-to-visible upconversion device 500 can be flipped or turned aroundand still function properly. For example, the substrate can be adjacentto the anode in FIG. 5B and adjacent to the cathode in FIG. 5C, suchthat FIG. 5B shows a similar configuration to that of FIG. 5C but withthe IR-to-visible upconversion device 500 turned around on thesubstrate. In the IR-to-visible upconversion device 500 depicted in FIG.5A, the substrate can be adjacent to the anode or the cathode. In aparticular embodiment, an IR-to-visible upconversion device 500 caninclude an interconnecting part 100 (as shown in FIG. 5A), and thesubstrate can be adjacent to the anode. IR light can be incident on theIR-to-visible upconversion device 500 from any direction, and visiblelight can be emitted from the IR-to-visible upconversion device 500 inany direction. The OLED 200 can be transparent to at least a portion oflight in the IR spectrum, though embodiments are not limited thereto.The photodetector 10 can be transparent to at least a portion of lightin the visible spectrum, though embodiments are not limited thereto.

Referring again to FIGS. 5A-5C, the IR-to-visible upconversion device500 functions by emitting visible light from the OLED 200 when thephotodetector 10 absorbs IR light. That is, the light sensitizing layer(e.g., an IR sensitizing layer) of the photodetector 10 absorbs IRlight, causing carriers to flow. The carriers flow to the OLED 200,either directly or via an interconnecting part 100, causing the LEL ofthe OLED 200 to emit visible light. The IR-to-visible upconversiondevice 500 can include a photodetector 10 with gain and canadvantageously exhibit gain.

Embodiments of the subject invention also relate to methods offabricating a photodetector with gain. The photodetector can be, forexample, an IR photodetector. In an embodiment, a method of fabricatinga photodetector with gain can include: forming a light sensitizing layeron a first electrode, forming an electron blocking/tunneling layer onthe light sensitizing layer, and forming a second electrode on theelectron blocking/tunneling layer.

The method can also optionally include forming the first electrode on asubstrate and/or forming a hole blocking layer on the first electrodesuch that the light sensitizing layer is formed on the hole blockinglayer. The substrate can be, for example, a glass substrate.

The first electrode can be a cathode, and the second electrode can be ananode. In an alternative embodiment, the first electrode can be ananode, and the second electrode can be a cathode. In certainembodiments, the first electrode and/or the second electrode can betransparent to at least a portion of visible and/or at least a portionof IR light, though embodiments are not limited thereto.

The first electrode can include one or more of the following materials:indium tin oxide (ITO), indium zinc oxide (IZO), aluminum tin oxide(ATO), aluminum zinc oxide (AZO), silver, calcium, magnesium. gold,aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, andCsCO₃/ITO. The second electrode can include one or more of the followingmaterials: ITO, IZO, ATO, AZO, silver, calcium, magnesium, gold,aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, andCsCO₃/ITO. In certain embodiments, the photodetector can be an IRphotodetector and the light sensitizing layer can be an IR sensitizinglayer. The light sensitizing layer can include, for example, one or moreof the following materials: PbS nanocrystals (quantum dots), PbSenanocrystals (quantum dots), PCTDA, SnPc, SnYc:C60, AlNCl, AlPcCl:C60,TiOPc, TiOPc:C60, PbSe, PbS, InAs, InGaAs, Si, Ge, and GaAs. In anembodiment, the electron blocking/tunneling layer can be a TAPC/MoO₃stack layer. The TAPC layer can be formed to a thickness of, forexample, 0 nm to 100 nm. The MoO₃ layer can be formed to a thickness of,for example, 0 nm to 100 nm.

In an embodiment, the method can include forming a hole blocking layer,and the hole blocking layer can include one or more of the followingmaterials: ZnO, NTCDA, BCP, UGH2, BPhen, Alq3, 3mCP, 3TPYMB, and TiO₂.

In a particular embodiment, the method of fabricating a photodetectorcan include: forming a light sensitizing layer on a first electrode,forming an electron blocking/tunneling layer on the light sensitizinglayer, and forming a second electrode on the electron blocking/tunnelinglayer. The electron blocking/tunneling layer can be, for example, aTAPC/MoO₃ stack layer, and the TAPC/MoO₃ stack layer can be formed suchthat the TAPC layer is formed directly on and in contact with the lightsensitizing layer and the MoO₃ layer is formed directly on and incontact with the TAPC layer. The second electrode can then be formeddirectly on and in contact with the MoO₃ layer of the TAPC/MoO₃ stacklayer. The light sensitizing layer can be, for example, an IRsensitizing layer and can include, e.g., PbS quantum dots. In a furtherembodiment, the method can include forming a hole blocking layer on thefirst electrode such that the light sensitizing layer is formed directlyon and in contact with the hole blocking layer.

Embodiments of the subject invention also relate to methods of detectingradiation using a photodetector with gain. The photodetector can be, forexample, an IR photodetector such that the method can detect IRradiation. In an embodiment, a method of using a photodetector with gainto detect radiation can include: providing a photodetector with gain,wherein the photodetector includes a first electrode, a lightsensitizing layer, an electron blocking/tunneling layer, and a secondelectrode. The photodetector can also optionally include a substrateand/or a hole blocking layer. The substrate can be, for example, a glasssubstrate.

The first electrode can be a cathode, and the second electrode can be ananode. In an alternative embodiment, the first electrode can be ananode, and the second electrode can be a cathode. In certainembodiments, the first electrode and/or the second electrode can be atransparent electrode.

The first electrode can include one or more of the following materials:indium tin oxide (ITO), indium zinc oxide (IZO), aluminum tin oxide(ATO), aluminum zinc oxide (AZO), silver, calcium, magnesium, gold,aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, andCsCO₃/ITO. The second electrode can include one or more of the followingmaterials: ITO, IZO, ATO, AZO, silver, calcium, magnesium, gold,aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, andCsCO₃/ITO.

In certain embodiments, the photodetector can be an IR photodetector andthe light sensitizing layer can be an IR sensitizing layer. The lightsensitizing layer can include, for example, one or more of the followingmaterials: PbS nanocrystals (quantum dots), PbSe nanocrystals (quantumdots), PCTDA, SnPc, SnPc:C60, AlPcCl, AlPcCl:C60, TiOPc, TiOPc:C60,PbSe, PbS, InAs, InGaAs, Si, Ge, and GaAs.

In an embodiment, the electron blocking/tunneling layer can be aTAPC/MoO₃ stack layer. The TAPC layer can be formed to a thickness of,for example, 0 nm to 100 nm. The MoO₃ layer can be formed to a thicknessof, for example, 0 nm to 100 nm.

In an embodiment, the photodetector can include a hole blocking layer,and the hole blocking layer can include one or more of the followingmaterials: ZnO, NTCDA, BCP, UGH2, BPhen, Alq3, 3mCP, 3TPYMB, and TiO₂.

In a particular embodiment, the photodetector can include: a lightsensitizing layer on a first electrode, an electron blocking/tunnelinglayer on the light sensitizing layer, and a second electrode on theelectron blocking/tunneling layer. The electron blocking/tunneling layercan be, for example, a TAPC/MoO₃ stack layer, and the TAPC/MoO₃ stacklayer can be positioned such that the TAPC layer is directly on and incontact with the light sensitizing layer and the MoO₃ layer is directlyon and in contact with the TAPC layer. The second electrode can then bedirectly on and in contact with the MoO₃ layer of the TAPC/MoO₃ stacklayer. The light sensitizing layer can be, for example, an IRsensitizing layer and can include, e.g., PbS quantum dots. In a furtherembodiment, the photodetector can include a hole blocking layer on thefirst electrode and under the light sensitizing layer.

Embodiments of the subject invention also relate to methods of formingan IR-to-visible upconversion device. The IR-to-visible upconversiondevice can be an IR-to-visible upconversion device with gain, and thephotodetector can be a photodetector with gain. In an embodiment, amethod of fabricating an IR-to-visible upconversion device can include:forming a photodetector with gain; forming an LED; and coupling the LEDand the photodetector with gain. The LED can be an OLED. Forming theOLED can include: forming at least one electrode, forming a holetransporting layer (HTL), forming a light emitting layer (LEL), andforming an electron transporting layer (ETL).

At least one electrode of the OLED can be transparent to at least aportion of visible and/or at least a portion of IR light, thoughembodiments are not limited thereto. Each electrode of the OLED caninclude one or more of the following materials: ITO, IZO, ATO, AZO,silver, calcium, magnesium, gold, aluminum, carbon nanotubes, silvernanowire, LiF/Al/ITO, Ag/ITO, CsCO₃/ITO, and a Mg:Ag/Alq3 stack layer,though embodiments are not limited thereto. The HTL of the OLED caninclude one or more of the following materials: NPD, TAPC, TFB, TPD, anddiamine derivative, though embodiments are not limited thereto. The LELof the OLED can include one or more of the following materials:Ir(ppy)3, MEH-PPV, Alq3, and Flrpic, though embodiments are not limitedthereto. The ETL of the OLED can include one or more of the followingmaterials: BCP, Bphen, 3TPYMB, and Alq3, though embodiments are notlimited thereto. In a particular embodiment, the electrode of the OLEDis a Mg:Ag/Alq3 stack layer.

The Mg:Ag layer of the Mg:Ag/Alq3 stack layer can have a composition of,for example, Mg:Ag (10:1) and can be formed to a thickness of, forexample, less than 30 nm. The Alq3 layer of the Mg:Ag/Alq3 stack layercan be formed to a thickness of, for example, from 0 nm to 200 nm.

The photodetector can be a photodetector with gain and can be formed asdescribed herein, though only one electrode need be formed. That is,forming the photodetector can include forming at least one electrode,forming a light sensitizing layer, and forming an electronblocking/tunneling layer. Forming the photodetector can also optionallyinclude proving a substrate and/or forming a hole blocking layer.

The electrode can be formed of one or more of the following materials:ITO. IZO, ATO, AZO, silver, calcium, magnesium, gold, aluminum, carbonnanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, and CsCO₃/ITO.

In certain embodiments, the photodetector can be an IR photodetector andthe light sensitizing layer can be an IR sensitizing layer. The lightsensitizing layer can be formed of, for example, one or more of thefollowing materials: PbS nanocrystals (quantum dots), PbSe nanocrystals(quantum dots), PCTDA, SnPc, SnPc:C60, AlPcCl, AlPcCl:C60, TiOPc,TiOPc:C60, PbSe, PbS, InAs, InGaAs, Si, Ge, and GaAs.

In an embodiment, the electron blocking/tunneling layer can be aTAPC/MoO₃ stack layer. The TAPC layer can be formed to a thickness of,for example, 0 nm to 100 nm. The MoO₃ layer can be formed to a thicknessof, for example, 0 nm to 100 nm.

In an embodiment, forming the photodetector can include forming a holeblocking layer, and the hole blocking layer can include one or more ofthe following materials: ZnO, NTCDA, BCP, UGH2, BPhen, Alq3, mCP,3TPYMB, and TiO₂.

In a further embodiment, coupling the photodetector with gain to theOLED can include coupling the photodetector with gain to aninterconnecting part and coupling the OLED to the interconnecting part.The photodetector can be coupled to the interconnecting part such thatthe electron blocking/tunneling layer of the photodetector is closerthan the light sensitizing layer is to the interconnecting part. TheOLED can be coupled to the interconnecting part such that the HTL of theOLED is closer than the ETL is to the interconnecting part. Thephotodetector can include an electrode under the light sensitizinglayer, and that electrode can be an anode. The OLED can include anelectrode on the ETL, and that electrode can be a cathode.

In an embodiment, coupling the photodetector with gain to the OLED caninclude coupling the photodetector with gain directly to the OLED. Thephotodetector with gain can be coupled to the OLED such that the ETL ofthe OLED is closer to the light sensitizing layer of the photodetectorthan it is to the electron blocking/tunneling layer of thephotodetector. In a particular embodiment, the photodetector can includea hole blocking layer adjacent to the light sensitizing layer, and thephotodetector with gain can be coupled to the OLED such that the ETL ofthe OLED is adjacent to and in contact with the hole blocking layer ofthe photodetector. The photodetector can include an electrode adjacentto and in contact with the electron blocking/tunneling layer, and theOLED can include an electrode adjacent to and in contact with the HTL.The electrode of the photodetector can be, for example, a cathode, andthe electrode of the OLED can be, for example, an anode.

Embodiments of the subject invention also relate to methods ofupconverting IR radiation to visible radiation using an IR-to-visibleupconversion device. The IR-to-visible upconversion device can include aphotodetector and an LED. The LED can be an OLED. The IR-to-visibleupconversion device can be an IR-to-visible upconversion device withgain, and the photodetector can be a photodetector with gain. The OLEDcan include at least one electrode, a hole transporting layer (HTL), alight emitting layer (LEL), and an electron transporting layer (ETL).

At least one electrode of the OLED can be transparent to at least aportion of visible and/or at least a portion of IR light, thoughembodiments are not limited thereto. Each electrode of the OLED caninclude one or more of the following materials: ITO, IZO, ATO, AZO,silver, calcium, magnesium, gold, aluminum, carbon nanotubes, silvernanowire, LiF/Al/ITO, Ag/ITO, CsCO₃/ITO, and a Mg:Ag/Alq3 stack layer,though embodiments are not limited thereto. The HTL of the OLED caninclude one or more of the following materials: NPD, TAPC, TFB, TPD, anddiamine derivative, though embodiments are not limited thereto, The LELof the OLED can include one or more of the following materials:Ir(ppy)3, MEH-PPV, Alq3, and Flrpic, though embodiments are not limitedthereto. The ETL of the OLED can include one or more of the followingmaterials: BCP, Bphen, 3TPYMB, and Alq3, though embodiments are notlimited thereto.

In a particular embodiment, the electrode of the OLED is a Mg:Ag/Alq3stack layer. The Mg:Ag layer of the Mg:Ag/Alq3 stack layer can have acomposition of, for example, Mg:Ag (10:1) and can have a thickness of,for example, less than 30 nm. The Alq3 layer of the Mg:Ag/Alq3 stacklayer can have a thickness of, for example, from 0 nm to 200 nm.

The photodetector can be a photodetector with gain as described herein,though only one electrode need be present. That is, the photodetectorcan include at least one electrode, a light sensitizing layer, and anelectron blocking/tunneling layer. The photodetector can also optionallyinclude a substrate and/or a hole blocking layer.

The electrode can include one or more of the following materials: ITO,IZO, ATO, AZO, silver, calcium, magnesium, gold, aluminum, carbonnanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, and CsCO₃/ITO.

In certain embodiments, the photodetector can be an IR photodetector andthe light sensitizing layer can be an IR sensitizing layer. The lightsensitizing layer can include, for example, one or more of the followingmaterials: PbS nanocrystals (quantum dots), PbSe nanocrystals (quantumdots), PCTDA, SnPc, SnPc:C60, AlPcCl, AlPcCl:C60, TiOPc, TiOPc:C60,PbSe, PbS, InAs, InGaAs, Si, Ge, and GaAs.

In an embodiment, the electron blocking/tunneling layer can be aTAPC/MoO₃ stack layer. The TAPC layer can have a thickness of, forexample, 0 nm to 100 nm. The MoO₃ layer can have a thickness of, forexample, 0 nm to 100 nm.

In an embodiment, the photodetector can include a hole blocking layer,and the hole blocking layer can include one or more of the followingmaterials: ZnO, NTCDA, BCP, UGH2, BPhen, Alq3, mCP, 3TPYMB, and TiO₂.

In a further embodiment, the IR-to-visible upconversion device can alsoinclude an interconnecting part between the photodetector and the OLED.The interconnecting part can be positioned such that the electronblocking/tunneling layer of the photodetector is closer than the lightsensitizing layer is to the interconnecting part, and the HTL of theOLED is closer than the ETL is to the interconnecting part. Thephotodetector can include an electrode under the light sensitizinglayer, and that electrode can be an anode. The OLED can include anelectrode on the ETL, and that electrode can be a cathode.

In an embodiment, the IR-to-visible upconversion device does not includean interconnecting part, and the photodetector is positioned directlyadjacent to the OLED. The OLED can be positioned such that the ETL ofthe OLED is closer to the light sensitizing layer of the photodetectorthan it is to the electron blocking/tunneling layer, of thephotodetector. In a particular embodiment, the photodetector can includea hole blocking layer adjacent to the light sensitizing layer, and theETL of the OLED can be positioned adjacent to and in contact with thehole blocking layer of the photodetector. The photodetector can includean electrode adjacent to and in contact with the electronblocking/tunneling layer, and the OLED can include an electrode adjacentto and in contact with the HTL. The electrode of the photodetector canbe, for example, a cathode, and the electrode of the OLED can be, forexample, an anode.

In many embodiments, the IR-to-visible upconversion device can beflipped or turned around and still function properly. The OLED can betransparent to at least a portion of light in the IR spectrum, thoughembodiments are not limited thereto. The photodetector can betransparent to at least a portion of light in the visible spectrum,though embodiments are not limited thereto.

The IR-to-visible upconversion device upconverts IR light to visiblelight. The IR-to-visible upconversion emits visible light from the OLEDwhen the photodetector absorbs IR light. That is, the light sensitizinglayer (e.g., an IR sensitizing layer) of the photodetector absorbs IRlight, causing carriers to flow. The carriers flow to the OLED, eitherdirectly or via an interconnecting part, causing the LEL of the OLED toemit visible light. The IR-to-visible upconversion device can include aphotodetector with gain and can advantageously exhibit gain.

EXAMPLE 1

A photodetector was fabricated on a glass substrate. The photodetectorincluded an ITO first electrode, a ZnO hole blocking layer on the firstelectrode, a PbS quantum dot light sensitizing layer on the holeblocking layer, a TAPC/MoO₃ stack electron blocking/tunneling layer onthe light sensitizing layer, and a second electrode on the electronblocking/tunneling layer. The PbS quantum dot light sensitizing layerhad the absorbance spectrum shown in FIG. 1A. The photodetectordisplayed the J-V characteristic curves (for dark and IR illumination at1240 nm and 0.302 W/cm₂) shown in FIG. 3B. Additionally, thephotodetector exhibited the gain and detectivity, as functions ofapplied voltage, shown in FIGS. 4A and 4B, respectively.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

1. A photodetector with gain, comprising: a first electrode; a lightsensitizing layer on the first electrode; an electron blocking/tunnelinglayer on the light sensitizing layer; and a second electrode on theelectron blocking/tunneling layer.
 2. The photodetector with gainaccording to claim 1, wherein the light sensitizing layer is sensitiveto photons having a wavelength in a range of from 0.7 μm to 14 μm,inclusive.
 3. The photodetector with gain according to claim 2, whereinthe light sensitizing layer is insensitive to photons having awavelength of at least 0.4 μm and less than 0.7 μm.
 4. The photodetectorwith gain according to claim 1, wherein the light sensitizing layercomprises PbS quantum dots or PbSe quantum dots.
 5. The photodetectorwith gain according to claim 1, wherein the light sensitizing layercomprises PbS quantum dots.
 6. The photodetector with gain according toclaim 1, wherein the light sensitizing layer comprises at least onematerial selected from the group consisting of PbS quantum dots, PbSequantum dots, PCTDA, SnPc, SnPc:C60, AlPcCl, AlPcCl:C60, TiOPc,TiOPc:C60, PbSe, PbS, InAs, InGaAs, Si, Ge, and GaAs.
 7. Thephotodetector with gain according to claim 1, wherein the firstelectrode comprises at least one material selected from the groupconsisting of indium tin oxide (ITO), indium zinc oxide (IZO), aluminumtin oxide (ATO), aluminum zinc oxide (AZO), silver, calcium, magnesium,gold, aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO,and CsCO₃/ITO.
 8. The photodetector with gain according to claim 1,wherein the second electrode comprises at least one material selectedfrom the group consisting of indium tin oxide (ITO), indium zinc oxide(IZO), aluminum tin oxide (ATO), aluminum zinc oxide (AZO), silver,calcium, magnesium, gold, aluminum, carbon nanotubes, silver nanowire,LiF/Al/ITO, Ag/ITO, and CsCO₃/ITO.
 9. The photodetector with gainaccording to claim 1, wherein the first electrode is an anode, andwherein the second electrode is a cathode.
 10. The photodetector withgain according to claim 9, wherein the first electrode comprises atleast one material selected from the group consisting of indium tinoxide (ITO), indium zinc oxide (IZO), aluminum tin oxide (ATO), aluminumzinc oxide (AZO), silver, calcium, magnesium, gold, aluminum, carbonnanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, and CsCO₃/ITO; andwherein the second electrode comprises at least one material selectedfrom the group consisting of indium tin oxide (ITO), indium zinc oxide(IZO), aluminum tin oxide (ATO), aluminum zinc oxide (AZO), silver,calcium, magnesium, gold, aluminum, carbon nanotubes, silver nanowire,LiF/Al/ITO, Ag/ITO, and CsCO₃/ITO.
 11. The photodetector with gainaccording to claim 1, wherein the electron blocking/tunneling layer is a1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC)/MoO₃ stack layer. 12.The photodetector with gain according to claim 11, wherein the TAPClayer is in direct contact with the light sensitizing layer, and whereinthe MoO₃ layer is in direct contact with the second electrode.
 13. Thephotodetector with gain according to claim 11, wherein the TAPC layerhas a thickness of no more than 100 nm, and wherein the MoO₃ layer has athickness of no more than 100 nm.
 14. The photodetector with gainaccording to claim 1, further comprising a hole blocking layer on thefirst electrode and under the light sensitizing layer.
 15. Thephotodetector with gain according to claim 14, wherein the hole blockinglayer comprises at least one material selected from the group consistingof ZnO, naphthalene tetracarboxylic anhydride (NTCDA),2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP),p-bis(triphenylsilyl)benzene (UGH2), 4,7-diphenyl-1,10-phenanthroline(BPhen), tris-(8-hydroxy quinoline) aluminum (Alq3),3,5′-N,N′-dicarbazole-benzene (mCP), C60,tris[3-(3-pyridyl)-mesityl]borane (3TPYMB), and TiO₂.
 16. Thephotodetector with gain according to claim 1, further comprising a glasssubstrate under the first electrode.
 17. The photodetector with gainaccording to claim 1, wherein the electron blocking/tunneling layer is aTAPC/MoO₃ stack layer, wherein the TAPC layer is in direct contact withthe light sensitizing layer, wherein the MoO₃ layer is in direct contactwith the second electrode, and wherein the light sensitizing layercomprises PbS quantum dots.
 18. The photodetector with gain according toclaim 17, further comprising a hole blocking layer on the firstelectrode and under the light sensitizing layer.
 19. A method offabricating a photodetector with gain, comprising: forming a firstelectrode; forming a light sensitizing layer on the first electrode;forming an electron blocking/tunneling layer on the light sensitizinglayer; and forming a second electrode on the electron blocking/tunnelinglayer.
 20. The method according to claim 19, wherein the lightsensitizing layer is sensitive to photons having a wavelength in a rangeof from 0.7 μm to 14 μm, inclusive.
 21. The method according to claim20, wherein the light sensitizing layer is insensitive to photons havinga wavelength of at least 0.4 μm and less than 0.7 μm.
 22. The methodaccording to claim 19, wherein the light sensitizing layer comprises PbSquantum dots or PbSe quantum dots.
 23. The method according to claim 19,wherein the light sensitizing layer comprises PbS quantum dots.
 24. Themethod according to claim 19, wherein the light sensitizing layercomprises at least one material selected from the group consisting ofPbS quantum dots, PbSe quantum dots, PCTDA, SnPc, SnPc:C60, AlPcCl,AlPcCl:C60, TiOPc, TiOPc:C60, PbSe, PbS, InAs, InGaAs, Si, Ge, and GaAs.25. The method according to claim 19, wherein the first electrodecomprises at least one material selected from the group consisting ofindium tin oxide (ITO), indium zinc oxide (IZO), aluminum tin oxide(ATO), aluminum zinc oxide (AZO), silver, calcium, magnesium, gold,aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, andCsCO₃/ITO.
 26. The method according to claim 19, wherein the secondelectrode comprises at least one material selected from the groupconsisting of indium tin oxide (ITO), indium zinc oxide (IZO), aluminumtin oxide (ATO), aluminum zinc oxide (AZO), silver, calcium, magnesium,gold, aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO,and CsCO₃/ITO.
 27. The method according to claim 19, wherein the firstelectrode is an anode, and wherein the second electrode is a cathode.28. The method according to claim 27, wherein the first electrodecomprises at least one material selected from the group consisting ofindium tin oxide (ITO), indium zinc oxide (IZO), aluminum tin oxide(ATO), aluminum zinc oxide (AZO), silver, calcium, magnesium, gold,aluminum, carbon nanotubes, silver nanowire, LiF/Al/ITO, Ag/ITO, andCsCO₃/ITO; and wherein the second electrode comprises at least onematerial selected from the group consisting of indium tin oxide (ITO),indium zinc oxide (IZO), aluminum tin oxide (ATO), aluminum zinc oxide(AZO), silver, calcium, magnesium, gold, aluminum, carbon nanotubes,silver nanowire, LiF/Al/ITO, Ag/ITO, and CsCO₃/ITO.
 29. The methodaccording to claim 19, wherein forming the electron blocking/tunnelinglayer comprises forming a TAPC/MoO₃ stack layer.
 30. The methodaccording to claim 29, wherein the TAPC layer is formed in directcontact with the light sensitizing layer, and wherein the secondelectrode is formed in direct contact with the MoO₃ layer.
 31. Themethod according to claim 29, wherein the TAPC layer has a thickness ofno more than 100 nm, and wherein the MoO₃ layer has a thickness of nomore than 100 nm.
 32. The method according to claim 19, furthercomprising forming a hole blocking layer on the first electrode, whereinthe light sensitizing layer is formed on the hole blocking layer. 33.The method according to claim 32, wherein the hole blocking layercomprises at least one material selected from the group consisting ofZnO, naphthalene tetracarboxylic anhydride (NTCDA),2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP),p-bis(triphenylsilyl)benzene (UGH2), 4,7-diphenyl-1,10-phenanthroline(BPhen), tris-(8-hydroxy quinoline) aluminum (Alq3),3,5′-N,N′-dicarbazole-benzene (mCP), C60,tris[3-(3-pyridyl)-mesityl]borane (3TPYMB), and TiO₂.
 34. The methodaccording to claim 19, wherein forming the first electrode comprisesforming the first electrode on a glass substrate.
 35. The methodaccording to claim 19, wherein forming the electron blocking/tunnelinglayer comprises forming a TAPC/MoO₃ stack layer, wherein the TAPC layeris formed in direct contact with the light sensitizing layer, whereinthe second electrode is formed in direct contact with the MoO₃ layer,and wherein the light sensitizing layer comprises PbS quantum dots. 36.The method according to claim 35, further comprising forming a holeblocking layer on the first electrode, wherein the light sensitizinglayer is formed on the hole blocking layer. 37-98. (canceled)